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><H1
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><A
NAME="CATALOG-PG-AGGREGATE"
>45.2. <TT
CLASS="STRUCTNAME"
>pg_aggregate</TT
></A
></H1
><P
>   The catalog <TT
CLASS="STRUCTNAME"
>pg_aggregate</TT
> stores information about
   aggregate functions.  An aggregate function is a function that
   operates on a set of values (typically one column from each row
   that matches a query condition) and returns a single value computed
   from all these values.  Typical aggregate functions are
   <CODE
CLASS="FUNCTION"
>sum</CODE
>, <CODE
CLASS="FUNCTION"
>count</CODE
>, and
   <CODE
CLASS="FUNCTION"
>max</CODE
>.  Each entry in
   <TT
CLASS="STRUCTNAME"
>pg_aggregate</TT
> is an extension of an entry
   in <TT
CLASS="STRUCTNAME"
>pg_proc</TT
>.  The <TT
CLASS="STRUCTNAME"
>pg_proc</TT
>
   entry carries the aggregate's name, input and output data types, and
   other information that is similar to ordinary functions.
  </P
><DIV
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><A
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></A
><P
><B
>Table 45-2. <TT
CLASS="STRUCTNAME"
>pg_aggregate</TT
> Columns</B
></P
><TABLE
BORDER="1"
CLASS="CALSTABLE"
><COL><COL><COL><COL><THEAD
><TR
><TH
>Name</TH
><TH
>Type</TH
><TH
>References</TH
><TH
>Description</TH
></TR
></THEAD
><TBODY
><TR
><TD
><TT
CLASS="STRUCTFIELD"
>aggfnoid</TT
></TD
><TD
><TT
CLASS="TYPE"
>regproc</TT
></TD
><TD
><TT
CLASS="LITERAL"
><A
HREF="catalog-pg-proc.html"
><TT
CLASS="STRUCTNAME"
>pg_proc</TT
></A
>.oid</TT
></TD
><TD
><TT
CLASS="STRUCTNAME"
>pg_proc</TT
> OID of the aggregate function</TD
></TR
><TR
><TD
><TT
CLASS="STRUCTFIELD"
>aggtransfn</TT
></TD
><TD
><TT
CLASS="TYPE"
>regproc</TT
></TD
><TD
><TT
CLASS="LITERAL"
><A
HREF="catalog-pg-proc.html"
><TT
CLASS="STRUCTNAME"
>pg_proc</TT
></A
>.oid</TT
></TD
><TD
>Transition function</TD
></TR
><TR
><TD
><TT
CLASS="STRUCTFIELD"
>aggfinalfn</TT
></TD
><TD
><TT
CLASS="TYPE"
>regproc</TT
></TD
><TD
><TT
CLASS="LITERAL"
><A
HREF="catalog-pg-proc.html"
><TT
CLASS="STRUCTNAME"
>pg_proc</TT
></A
>.oid</TT
></TD
><TD
>Final function (zero if none)</TD
></TR
><TR
><TD
><TT
CLASS="STRUCTFIELD"
>aggsortop</TT
></TD
><TD
><TT
CLASS="TYPE"
>oid</TT
></TD
><TD
><TT
CLASS="LITERAL"
><A
HREF="catalog-pg-operator.html"
><TT
CLASS="STRUCTNAME"
>pg_operator</TT
></A
>.oid</TT
></TD
><TD
>Associated sort operator (zero if none)</TD
></TR
><TR
><TD
><TT
CLASS="STRUCTFIELD"
>aggtranstype</TT
></TD
><TD
><TT
CLASS="TYPE"
>oid</TT
></TD
><TD
><TT
CLASS="LITERAL"
><A
HREF="catalog-pg-type.html"
><TT
CLASS="STRUCTNAME"
>pg_type</TT
></A
>.oid</TT
></TD
><TD
>Data type of the aggregate function's internal transition (state) data</TD
></TR
><TR
><TD
><TT
CLASS="STRUCTFIELD"
>agginitval</TT
></TD
><TD
><TT
CLASS="TYPE"
>text</TT
></TD
><TD
>&nbsp;</TD
><TD
>       The initial value of the transition state.  This is a text
       field containing the initial value in its external string
       representation.  If this field is null, the transition state
       value starts out null.
      </TD
></TR
></TBODY
></TABLE
></DIV
><P
>   New aggregate functions are registered with the <A
HREF="sql-createaggregate.html"
>CREATE AGGREGATE</A
>
   command.  See <A
HREF="xaggr.html"
>Section 35.10</A
> for more information about
   writing aggregate functions and the meaning of the transition
   functions, etc.
  </P
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